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Book Summary: War – How Conflict Shaped Us by Margaret MacMillan

War (2020) is a philosophical inquiry into the nature of human conflict. It considers war from different angles, examining what causes it, how we think about it, and how it affects us. By making an effort to understand war, we become better prepared to avoid it.

Who is it for?

  • Students of international and military history
  • People interested in cultural and philosophical differences
  • Anyone fascinated or affected by human conflict

Explore the debate about why and how humans make war.

What emotions do you feel when you hear the word war? Is it a sense of horror and dread? Or perhaps admiration –⁠ a feeling that war can be exciting or even glamorous?

War is obviously a complex subject, both emotionally and intellectually. Throughout the course of history, humans have been both making war and theorizing about it. And while war brings violence, destruction, and cruelty, it’s also shaped society as we know it.

We shouldn’t view peace as the norm and war as an aberration. Rather, we should explore how war and human society have evolved together – as we’ll do in this summary. If we learn to understand war, we can also learn to avoid it.

Book Summary: War - How Conflict Shaped Us by Margaret MacMillan

In this summary, you’ll find out

  • whether humans are more like chimps or bonobos;
  • how a ship captain’s ear started a war; and
  • why we tend to view World War I so negatively.

Humans have always made war – and we may be genetically programmed to do so.

Nestled in the Swiss alps is the quaint town of Bolzano. One of its major attractions is Ötzi, otherwise known as the Iceman. Ötzi is the mummified corpse of a man who lived around 3300 BC, well before the Great Pyramids were constructed in Egypt or Stonehenge was built in ancient Britain.

How did Ötzi die? At first, archaeologists thought that he’d gotten lost in the mountains and frozen to death. But eventually they discovered something very different: Ötzi’s body was covered in cuts and bruises, and an arrowhead stuck out from his shoulder. His own knife and arrowheads had blood on them. So it seems Ötzi died in a fight.

His story shows that humans have been wounding and killing each other since at least the later Stone Age. But why?

The key message here is: Humans have always made war – and we may be genetically programmed to do so.

For decades, scientists believed that early humans lived peaceful, nomadic hunter-gatherer lives. But now, researchers are almost certain that organized, armed conflict has always been part of our existence.

Does that mean war is encoded in our biology? Are we genetically programmed to fight? To discover the answer to that question, scientists have studied chimpanzees and bonobos – humans’ closest genetic relatives.

What they’ve found is, unfortunately, inconclusive. On the one hand, chimps can be quite violent. They start deadly conflicts with little or no provocation. The bonobos, on the other hand, are seemingly much more peaceful. When two bonobos first meet, for instance, they gaze at one another, share food, and embrace rather than attack.

So which one is more like us? The answer may be neither. That’s because, as history clearly shows, humans are capable of both extreme violence and far-reaching cooperation.

We’re still driven by the same evolutionary forces that shaped our species at the dawn of humanity. Some of them – like the desire for food – can make us violent. But we have also, in a sense, domesticated ourselves. We can choose not to go to war, or we can go to war in service of more abstract ideas, like honor or religion.

Let’s dive a little deeper into reasons for war.

Wars are motivated by greed, self-defense, emotions, and ideas.

In 1731, a British seafarer, Captain Jenkins, lost his ear. He claimed that Spanish sailors had cut it off after accusing him of smuggling. Jenkins complained to the English king, but, for seven years, nothing happened. Eventually, the captain produced what he said were the remains of his ear. And the following year, in 1739, Britain went to war with Spain.

Jenkins’ ear was, of course, merely an excuse to start the war. In reality, Britain had other motives, like its desire to enter lucrative trade with the West Indies and Spanish America. Meanwhile, the Spanish wanted to preserve their monopoly in the region.

Sometimes, as with Jenkins’ ear, the grounds for war can seem pretty absurd. But more serious tensions usually simmer below the surface.

Here’s the key message: Wars are motivated by greed, self-defense, emotions, and ideas.

The list of reasons for starting a war is long. From assassinations to imperialism, romance to religion, there is no shortage of motivations. Still, we can pick out a few key themes that tie most wars together; greed, self-defense, emotions, and ideas.

Let’s start with greed. Consider, for instance, the Mongols, whose empire sprawled across Eurasia throughout the thirteenth and fourteenth centuries. Their wars grew from the desire to plunder and loot. Or take Saddam Hussein, who attempted to seize Kuwait in the 1990s because of the country’s oil riches.

Then there’s self-defense. Over the years, societies have gone to war in response to threats, both real and imagined. Look at the case of Israel, for example. The country attacked Egypt, Syria, and Jordan in 1967. It had good reason to believe the three countries were planning a joint attack – a very real threat.

And then, by contrast, consider Hitler. The Nazi dictator had many reasons for war, but one of them was a completely unfounded, irrational fear. Hitler thought that the peace in Europe was making Germans soft and weak. In his fantasy world, Hitler thought war would toughen up his countrymen.

Finally, humans have gone to war because of emotions and ideas. Napoleon, Alexander the Great, Louis XIV – all of these men sought personal glory rather than societal benefit. And it’s not just about leaders. Religion, politics, and nationalism have also inspired countless ordinary men and women to fight to the death.

A society’s institutions, values, and beliefs all influence the way it views and fights wars.

If you’re at all interested in the European Middle Ages, chances are you’ve heard the legend of King Arthur and the Holy Grail.

In the medieval period, stories like this were told and retold by generations of young men. They looked up to knights like Launcelot and Galahad for their honor and virtue, as well as their battlefield skills. The very idea of being a hero was a cornerstone of chivalry, a culture that encouraged men to prove their valor. The reward was usually a woman’s hand in marriage.

This was, of course, a romantic way of viewing wars. In reality, conflict was bloody, violent, and brutal. But culture reframed reality in the Middle Ages, just as it has at other times.

The key message is this: A society’s institutions, values, and beliefs all influence the way it views and fights wars.

Many cultures throughout history have venerated war. Take the Roman Republic. In its early years, male citizens were obliged to serve sixteen years in the military, and had to serve at least ten before they could hold political office. Later in the Republic, some of the fighting was outsourced to mercenaries – but war still permeated the culture. Just think about the lavish triumphs, festivals that victorious generals organized for the entire city as they returned to Rome with the spoils of war.

Aside from glorifying war itself, cultures can also venerate particular types of battle tactics or strategies.

In sixth-century China, for instance, the military general and philosopher Sunzi promoted the idea of winning battles without bloodshed. That idea had major staying power; subsequent Chinese dynasties often used walls and bribery to keep out invaders. Armed forces remained their last resort.

Culture can even affect the technology of war.

For an example, let’s return to ancient Rome. For centuries, its peasants had been using levers to press grapes for wine and olives for oil. Roman soldiers repurposed those same levers to build ships and fortifications, and to hurl stones at enemies.

Technologies like these can help one culture against another. And there are times when culture itself can serve as a kind of weapon. For instance, the Spanish were, in part, victorious over the Incas because they managed to abduct the Incan emperor. This violated the rules of Incan society and left the nation without a leader. For such a hierarchical state, it was a huge blow.

Nationalism, the Industrial Revolution, and cultural changes shaped modern warfare.

The date: September 20, 1792. The place: Valmy, a small village in eastern France.

The French army –⁠ poorly equipped and badly organized –⁠ is going head-to-head with the highly disciplined Prussians. The French sustain greater casualties, yet the Prussian forces are being depleted by dysentery. The Prussians ultimately decide to retreat.

Neither side can justifiably claim victory. Nevertheless, the poet Goethe claims that the battle has marked out “a new era in the history of the world.”

This was not hyperbole. The battle at Valmy marked the beginning of what we know today as nationalism: something that brings a group of people from a certain geographic area together, and encourages them to self-identify as a collective. Today we’d call this collective a nation.

Nationalism is one of three factors that have made modern warfare so violent, deadly, and destructive.

The key message here is: Nationalism, the Industrial Revolution, and cultural changes shaped modern warfare.

Prussians and other observers were alarmed by the French fighting style: they sang songs during battles and fought savagely to the death. They were an army of common citizens motivated by a passionate belief in their nation’s cause –⁠ unlike the Prussians, an army of professional soldiers motivated by fear of their own officers.

Nationalism brought citizens together to fight for a common goal. It also promoted the idea that it was a person’s duty to come to the defense of his nation. As a result, it inspired people to join wars that otherwise would have remained irrelevant to them.

In the early nineteenth century, there was also another force shaping the face of war: the Industrial Revolution. It brought about a surge of innovation and a major increase in production capacity. These effects naturally spread to the military.

The Industrial Revolution didn’t just mean better guns. It also increased the size and spending power of the middle and working classes. As a result, the masses felt that now they, too, had the right to voice their views about war. Discussing conflict was no longer just for the elites.

With these factors combined, modern war transformed into something all-consuming – what we now call total war.

It exists on a scale previously unimaginable. Armies now consist of millions of soldiers – an order of magnitude more than before. Countries must harness their entire economic might to serve war efforts.

And, as the resources of the military have grown, so have the armies’ capacity for death and destruction. In modern times, war brings about more suffering than people ever thought possible.

People can be persuaded –⁠ or forced –⁠ to fight in wars for a variety of reasons.

On March 29, 1461, two English royal houses, the Yorks and the Lancasters, fought the Battle of Towton. It was, and remains, the bloodiest battle ever fought on English soil. Fifty thousand soldiers participated, and as many as 28,000 of them died. The violence was so astonishing that the field on which that battle occurred came to be known as the Bloody Meadow.

Wars are undeniably bloody. And yet men, and sometimes women, have consistently been drawn to fight in them. Why?

Here’s the key message: People can be persuaded –⁠ or forced –⁠ to fight in wars for a variety of reasons.

People haven’t always voluntarily gone to war. In eighteenth-century Europe, for instance, criminals were offered one of two options: be executed or join the military.

But not everybody has to be forced into the army. There are plenty of reasons why people actively choose to join a war. Poverty is one. Today, the American military often focuses its recruitment efforts in poorer areas, where people are desperate for regular pay and sometimes even food. The Forces can provide both.

Another thing that can inspire – or deter – people from joining the military is culture. In many societies, young boys are expected to display warrior-like qualities before they can be considered men. Naturally, this encourages many to join the military.

Culture, however, doesn’t always fully prepare young people to become soldiers. Other traditions help draw a clear distinction between civilian and military life. This is the origin of uniforms and mandatory crew cuts. In Roman legions, standards –⁠ bronze or silver eagles –⁠ were used to forge a shared identity among the soldiers.

Once a person has joined the military, of course, that’s far from the end of the story. The new soldier must then also be trained to keep fighting, even when the instinct might be to flee. Often, discipline is enforced by threats. In Trotsky’s Red Army, for instance – the Soviet Army of the early twentieth century – commissars used battlefield executions to discourage soldiers from retreating. Clearly, bravery and courage aren’t the only things that keep a soldier fighting.

When we think about war, we often focus on soldiers, people on the front lines. But we sometimes forget another group, which plays a different, yet equally significant, role: civilians.

We’ll explore what war means for them in the next chapter.

Civilians can benefit from war, but they’re also subject to some of its greatest horrors.

Civilians are a special category of people during times of war, and various sets of rules have attempted to define how they should be treated. Usually, these rules declare that civilians and their property should not be harmed. But, of course, regulations tend to go out the window in the heat of battle.

In the age of modern warfare, military strategists sometimes coldly refer to civilians as the “collateral damage” that results from war. When their side is defeated, civilians may be killed, enslaved, or deported. But war isn’t always bad for them – in fact, it can sometimes provide benefits, like opportunities to make money. And civilians aren’t always passive bystanders. Often, they have great passion for war, just like the soldiers themselves.

The key message is this: Civilians can benefit from war, but they’re also subject to some of its greatest horrors.

Female civilians have often been subjected to a particular torment –⁠ rape. In World War II, for instance, Stalin defended Soviet soldiers who’d raped civilians in cities they liberated from the Nazis. In fact, it’s estimated that the Soviets raped as many as two million women in a single year in Germany alone.

On the flip side, wars have also brought women some major gains – such as rights, education, and careers. At the start of World War I, women made up 23 percent of the labor force in British industry and transport. By 1918, that number had shot up to 34 percent, as women filled in for men who’d gone off to fight. Then, of course, they faced new challenges, like unequal pay and mistreatment by male colleagues. In one instance, some male employees at a factory in Birmingham deliberately sabotaged machinery to slow down their female colleagues.

While civilians today often deal with the economic consequences of war, they can also become targets in combat, as strategists seek ways to weaken the enemy. In the American Civil War, for example, General Sherman targeted civilians by burning buildings, stealing their farm animals, and destroying their crops. He was convinced that this would cut off a major line of support to the opposing Confederate side.

War does not allow civilians to decide whether or not they want to participate. And as modern war has expanded, their roles have only increased. After all, war requires people who can make bullets just as much as it needs soldiers who can fire them.

Humanity has repeatedly attempted to construct rules around organized conflict.

A young Harvard graduate named John Reed traveled to Mexico in 1913. For four months, he accompanied a Mexican rebel leader called Pancho Villa. One day, Reed showed Villa a curious pamphlet. It outlined the new rules of war adopted at the Hague Conference in 1907.

Villa was very interested in the pamphlet and pored over it for hours. But he couldn’t understand the motivation for making rules about war. “It is not a game,” he said. “What is the difference between civilized war and any other kind of war?”

Villa’s query neatly identifies one of the paradoxes of war. If we accept that war is all about violence and domination, how can it possibly be something we can try to control or manage?

The key message here is: Humanity has repeatedly attempted to construct rules around organized conflict.

Aggressors often rely on rules to justify the act of making war in the first place.

For just one example, take the invasion of the Chinese state of Shang by the duke of Chou in 1122 BC. The duke argued that heaven had revoked the Shang ruler’s mandate because he was a drunkard and a tyrant. Conveniently, heaven had supposedly given that mandate to the duke of Chou instead.

These days, in place of religion, we use a system of laws, ethics, and morality to make rules around war. Among the less controversial of these is the idea that self-defense is a legitimate reason for war. But even this rule raises the question of whether societies are justified in starting preventative wars. What if you merely think that you’re about to be attacked? Should you strike first?

And it’s not only wars themselves that we’re trying to regulate. The world has also debated the use of particular types of weaponry. In the twenty-first century, we consider chemical poisons or biological agents beyond the pale. And yet firebombs and flamethrowers are considered acceptable – even though they, too, are designed to kill or injure.

There have also been attempts to bring in rules about the tactics of war. In 1856, for instance, the Declaration of Paris outlined rules for naval blockades. These limited their use as a tool for seizing goods from enemy or neutral ships.

So laws regulate the conduct of modern war. There is now a whole web of norms, from written international agreements to unspoken customs. But these rules only last until war actually comes –⁠ and then, it’s utter chaos.

The experience of war, and the ways it’s depicted in art, are deeply varied.

What sensations, smells, sights, and emotions characterize fighting? There isn’t just one answer.

The ancient Greeks, for instance, had a rather dispassionate way of describing battle. Wounds were merely catalogued: a spear piercing a groin here, an arrow sticking someone in the eye there.

Death was ordinary –⁠ a natural and normal fate for a warrior.

But now, there’s a lot of disagreement about how to portray war. Painters, writers, and filmmakers have their own artistic priorities. But soldiers, people on the front lines, can describe conflict entirely differently.

Here’s the key message: The experience of war, and the ways it’s depicted in art, are deeply varied.

Across history and geography, soldiers have reported a vast variety of battlefield experiences. One Soviet woman fighter, for instance, mostly remembers fear. In her very first battle, she says, her heart felt as if it were “about to burst,” and her skin “ready to split.” By contrast, a Canadian general describes the terrible thrill of battle. To him, this adrenaline rush was only made stronger by the knowledge that he could die at any moment.

In art, too, depictions of battle are rich and varied. Some, like the opening scene of Apocalypse Now, a film about the Vietnam War, show the terrible beauty of warfare. Other art, like Francisco Goya’s The Disasters of War, depicts a colorless scene, emphasizing the devastation and destruction of conflict.

When it comes to war, our memories are often selective. The way we think about conflicts is deeply shaped by events that happen after them. Look at how differently we perceive the two world wars of the twentieth century, for example. World War II is seen as a straightforward battle of good versus evil. And that view casts a shadow on our thoughts about World War I, a conflict that seems foolish and immoral in comparison.

What we forget is that many of the soldiers who fought in World War I did believe they’d gone to war for something worthwhile. If nothing else, they were fighting for the safety of their loved ones.

All these differences teach us a valuable lesson. We should be careful about how we represent war and how we think about it. If we paint conflicts with a broad brush, we ignore their complexity. But we mustn’t forget that war can encompass extremes: beauty and horror, wickedness and nobility, destruction and creativity.


The key message in these summary:

For better or worse, war has shaped the course of human history. We have made war for all sorts of reasons: to get resources, to advance religion, even to win personal glory. And as humans fought in countless wars, conflict altered the lives of both civilians and soldiers. Modern war has particular impact, as nationalism, the Industrial Revolution, and societal changes have massively increased the scope of armed confrontation. If we fail to examine the causes of war and the reasons we fight, we will hinder our ability to avoid war in the future.

About the author

Margaret MacMillan is a historian, professor emerita of international history at Oxford University, and professor emerita of history at the University of Toronto. In 2018, she was the Reith lecturer, giving talks in five major cities on the subject of war. She is also a fellow of the Royal Society for Literature and the best-selling author of Paris 1919, which won numerous awards, and The War That Ended Peace, which was named a New York Times Notable Book.

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